Abstract: In this paper, piecewise potential vorticity (PV) inversion method is used to carry out inversion on the quasi-stationary mesoscale vortex (hereinafter called Guangxi vortex) in the process of Guangxi flashflood rainstorm in June 2006, and contributions of various PV perturbations with different physical properties on the Guangxi vortex are diagnostically analyzed. The results show that the wet PV perturbation Qhrelated to latent heat release had direct effect on the Guangxi vortex and it played as the major positive contribution on the development of the vortex. Its contribution was concentrated on low-to-mid troposphere. While the contribution of dry PV perturbation Qh, no relation with latent release, was mainly concentrated on mid-to-high troposphere. It was favorable for the Guangxi vortex to extend to high level and deepen.Both Qh and Qd had influence on the tracks of the vortex.